This year, our group published 10 scientific articles related to DNA replication and its fidelity. We previously showed that ribonucleotides incorporated during eukaryotic nuclear DNA replication are subject to removal by a mutant derivative of RNase H2 that is defective in repairing ribonucleotides incorporated during yeast DNA replication. We showed that such strains have high mutation rates for deletion of 2-5 base pairs due to incision of newly incorporated rNMPs by DNA topoisomerase 1. This year we described this mutagenesis across the entire yeast genome. Using RNase H2 mutant strains with an additional mutation in each of the three major replicative DNA polymerases, we extended our previous studies by showing that DNA polymerase delta is involved in initiating and terminating leading strand replication, and that it is also the major polymerase involved in break-induced replication at chromosome ends. We collaborated with two other groups to describe the X ray crystal structure of DNA polymerase mu bound to a ribonucleotide. We also extended earlier work on the properties of a yeast strain lacking the catalytic activity of Pol epsilon, and demonstrated that polymerase epsilon activity is important for accurate replication of the majority of leading DNA strand synthesis and that in its absence, DNA polymerase zeta conducts error prone replication. We also collaborated with two other principal investigators to show that RNH-H2 is a tumor suppressor genes for skin and colon cancer in mice, we published two review articles in the DNA replication field, and we published an article showing the X-ray crystal structure of DNA polymerase mu performing mutagenic incorporation of adenine opposite 8-oxo-guanine during nonhomologous end-joining of double-strand DNA breaks.